Automatically retractable spark plug for gas turbines



D. C. BERKEY July 22, 1952 AUTOMATICALLY RETRACTABLE SPARK PLUG FOR GAS TURBINE-S Filed Nov. 30, 1949 Inventor:

W k V./ m 6. r w w d t. IA a n m o D.H Y b ual motion initially caused by gas'pressure acting on protrustion I!) alone.

Coil spring 22 is disposed within skirtil of piston 9, and is under compression between cap 8 of the cylinder and end 18 of the piston. The spring is under sufficient compression to hold end l8 of the piston against the flange l, forcing protrusion and electrode member l5a carried thereby into the combustion chamber. The spring force is opposed by. normal operating pressure within the combustion chamber to an extent that permits electrodes 48, l I to be removed from the hot gas stream when the combustion chamber comes up to normal operating pressure during the starting cycle.

" Any of the hot'g'ases that may leak between the skirt I! of the piston and the wall of the body portion 6 escape through the openings 16 in cap 8 to the atmosphere.

Igniter [5 comprises the first electrode assembly [5b, the second electrode assembly l5a, connectedelectrically by a pair of telescoping electrodes 23, 24. a

Electrode assembly I522 comprises an insulator 210i porcelain or the like having a central opening 21a extending axially therethrough. Insu lator 21 is inserted through central opening l4 provided in cap 8 and is separated from direct contact therewith by a gasket 23. Abushing .30, having an axial bore 3| large enough to accommodate an extended portion 32 of insulator 21, is inserted over extended portion 32 and a threaded portion 33 on bushing 38 engages a threaded portion of opening [4 in end cap 8 to rigidly secure insulator 21 to end cap 8. Bushing 30 is further provided at its upper end with a threaded portion 26 for engaging a conduit (not shown) adapted to conduct. a high voltage ignition cable (not shown) into opening, 28 in insulator 21. I g l The second electrode assembly l5a of igniter I5 is generally similar in construction to the first portion I517. Portion 15a is provided with an insulator 34 which extends through protrusion ID on piston 9. Insulator 3 1 is cushioned from direct contact with protrusion It by gasket 23. A bush- 7 ing 35', having a central opening large enough to accommodate extended portion 36 of insulator 34, is inserted thereover and its threaded portion 3! is brought into engagement with the threaded portion of bore 19. I r

The hollow electrode 23 fits securely in a bore v through insulator 21. and extends axially therefrom towards portion I 5a. A central axial opening 38 extends completely through electrode 23. Electrode 23 issecured in insulator 21 by a cap 39 which is arranged to contact the high voltage cable terminal connected to threaded fitting 26. 'Ihemovableelectrode 24 has anenlarged portion!!! extending through a central bore 4| in insulator 34 and is sealed in place by a sleeve 4 I a.

a A reduced electrode portion 42 extends from base portion into'the bore 38 in electrode 23. Reduced portion '42 -is ;:freely slidable in bore 38 of electrode 23. vAny air gap which may exist between reduced portion 42 and the bore 33 is easily of piston 9 and cap member 3 is screwed onto housing 6. The first'electrode assembly l5b of the igniter is then inserted through the aperture [4 in cap member 8, electrode 23 coming into telescoping engagement with the movable electrode24. After securing housing 6 to the combustor wall, a high tension power cable (not shown) may be removably connected to the fitting 25 at the end of igniter l5. Then when a high voltage is applied to the power cable, current travelsdown electrode 23, across the gapv formed by the telescoping portionsof the electrodesand out through electrodeZd to the spark gap defined by electrodes 40, H. 3

1 In operation, this retractable spark plug func tions in the following manner. To starta gas turbine of the type described, a-starting motor (not shown) cranks? an air compressor (not shown); Ilhe cranking speed is adequatexto force some air'through inlet il in combustion chamber 2, thence through outer passageway I3 and openings I3a into the actual combustion space 5. The air pressure built upby thestarting motor driving the compressor is notgreat enough to eiiect movement of protrusion Ill against the bias of spring 22; but it is 'sufiicient to initiate self-sustaining combustion. Fuel is now injected throughnozzle 3 into this compressed-air, and the mixture is ignited by a spark across electrodes Gil, I l of the igniter. The products of combustion from'the burning so initiated drive a gas turbine (not'shown) whichis directly connected to the air compressor that supplies compressed air to opening 4 of the combustion chamber. The gas turbine gradually increases in speed, in turn buildingup the discharge pressure of the air compressor and that of the airin passageway 4 until normal operating speed of the turbine is reached.

Spring 22 withinthe automatically retractable spark plug is adapted to maintain the piston l! in the position shown in Fig. 2 at all pressures below normal operating pressure of the combustion chamber. Consequently, the electrodes 40, remain in the combustion space untilnormal pressure is reached, whereupon; the, pressure acting on thebottom of protrusion H1 forces piston 9 away from flange 1. The motion of protrusion if] out of the combustion space is at a slow rate as compressor discharge pressure gradually increases until shoulder 2i on protrusion I!) passes the inner edge of openingla Then, 'however the air pressure acts on the total bottom surface l8 of thepiston member 9. This. greatly increased; force rapidlyretracts the igniter points 40, ll out of the hot'combustion chamber and into the cool air stream traveling from inlet 4 through pas-- The limiting position is so arranged, however, that the ignition points are completely withdrawn from the actual combustion space and into the cool air stream passing through passageway l3.

Any compressed air or gases that pass extended portion l5b of the igniter or which pass skirt ll of piston member 9 into body portion 6 exit to the atmosphere through apertures 16 in cap 8. The withdrawal of the protrusion from the hot combustion chamber keeps the electrodes 40, H of the igniter from carbonizing, thus maintaining them in good operating condition much longer than if they were continuously exposed to the hot gas stream within the combustion space.

While for convenience in description the combustion supporting fluid is referred to as air,

it will be obvious that the igniter of this invention may be equally applicable to other thermal reaction devices, such as rocket motors, in which other fluid reactants are used.

Modifications of this invention will occur to those skilled in the art and it is desired to be understood, therefore, that this invention is not to be limited to the particular arrangement disclosed, but that the appended claims are meant to cover all modifications which do not depart from the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric ignition device for combustion apparatus to which a pressure fluid is supplied during normal operation and discontinued when the apparatus is shut down comprising a cylin drical body member having one open end and a central opening in the other end, a piston member slidably disposed in the body and having a protruding end portion, means resiliently biasing the piston to an extended position in which the protruding piston portion projects through said central opening, an end cap closure member secured to the open end of the body and having a central opening and at least one pressure relief passage therethrough, a first insulated electrode assembly secured in the central opening of the end cap and having a firstelectrode projecting axially into the housing, a second insulated electrode assembly secured in a central bore through the protruding piston portion and having a second electrode with a first end portion projecting from the exterior end of the assembly and defining a spark gap with a grounded electrode carried by the piston protrusion, said second electrode having a second end portion slidably engaging the first electrode in electrical conducting relation therewith for all positions of the movable piston, the body being adapted to be secured to the combustion apparatus with the protruding piston end portion subjected to the pressure of the fluid supply whereby during normal operation said pressure will maintain the piston in retracted position.

2. An electric ignition device in accordance with claim 1 in which the protruding piston end portion has at least one circumferential portion cooperating with the body to define a passage for communicating fluid pressure to the entire end surface of the piston and a cut-off portion adapted to interrupt such communication of pressure fluid to the piston when in fully extended position, whereby the pressure fluid will initially act on the protruding piston end portion only and initial movement of the piston against the bias of the resilient means efiects communication of pressure fluid through said passage to cause further rapid movement of the piston to the fully retracted position.

3. An electric ignition device in accordance with claim 1 in which the slidably engaged electrode portions are in telescopic relation.

DONALD C. BERKEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,208,926 Dick Dec. 19, 1916 1,764,984 Rogers et al June 17, 1930 1,845,305 Macrae Feb. 16, 1932 2,119,952 Engels June 7, 1938 2,441,284 Parrish May 11, 1948 2,493,743 Benson Jan. 10, 1950 FOREIGN PATENTS Number Country Date 585,343 Great Britain .1 Feb. 5, 194? 

